The present disclosure generally relates to displays, and specifically relates to holographic displays in head-mounted displays.
There are various forms of display technology that can be found in conventional head-mounted displays (HMDs). Computer generated holography is one such technology, however, while having relatively good resolution it has a very limited field of view. Computer generated holography is a way of generating a computer generated hologram. A difference between the traditional hologram and a computer generated hologram is how the original images are created. A traditional hologram is a holographic interference pattern of light from a real object and light from a coherent source. In contrast, a computer generated hologram may be calculated using known algorithms that simulate the holographic interference pattern of a traditional hologram. A virtual object can later be re-constructed using a coherent source and the computer generated hologram presented using a spatial light modulator (SLM).
HMDs in virtual reality systems and/or augmented reality systems typically have very large fields of view (e.g., 110 degrees or more). Construction of a virtual image using a computer generated hologram results in multiple diffractive orders of the virtual image that overlap spatially. In order to avoid overlap of diffractive orders and achieve a high field of view a pitch size of a SLM is approximately as small as a wavelength of the coherent source (e.g., 500 nanometers), whereas state-of-the-art SLMs have pitch sizes of about 3 micrometers (would correspond to about an 8 degrees of horizontal or vertical field of view). Accordingly, conventional computer generated holography systems are unable to provide large fields of view that are expected of HMDs for virtual reality and/or augmented reality applications.